are copods bad?

[Amphiprion]

Well, copepods are much, much smaller than amphipods. In fact, copepods almost show up as small specks--barely visible. Amphipods are much larger and more visible. There are exceptions to what I've described, but for all intents and purposes, that is the case.

 

[FinFanatic]

Be careful. One mandarin can wipe out an entire amphipod colony in no time. Many mandarins eat only amphipods. When they're gone, the mandarins starve to death.
You might want to try and get your mandarin to eat frozen foods as well (if possible, if it doesn't already).